It is a self supporting rubber band powered engine shaft and blade. It is designed to fit a specific type of balsawood aircraft sold at Michael's craft store, but im sure it will fit any old thing you strap it to. Now you can play with the r-band powered craft as much as you want, and when it breaks, you can simply switch the prop over to a new plane! Here's how to make it....
1 proconstructed balsa wood airplane (I got mine from MIchael's crafts for $1)
1 long and one small rubberband
1 or 2 Lego propellers (the bigger the better)
a small paperclip
less than a foot of 1/4" dowel rod (use poplar or pine)
certain common Legos, pictured below
a dremel tool or something with simiar drilling and sanding capabilities
silicone spray makes it much faster
remove the nose weight
Step 1: Making the rotary shaft
1. get out your long rubberband and the three other legos pictured. A black ridged rod about an inch long, a gray friction nut, and a cylindrical hollow uni-bumb.
2. cut your rubberband and slide the ends through the top of the black uni-bumb.
3. slide the black uni-bump with the band in it onto the black ridged rod in such a way that the rubberband is also attached to the rod. Slide the gray friction nut onto the shaft, and put superglue between the nut and black uni-bump to help permanently attach these items to the black ridged rod.
4. (note in the photo i used a cylindrical unibump for this part, you should use two cubic unibumps)
get two cubic uni-bumps. you can lego lock them and glue them together to that the holes are facing the same direction.
5. Now get your propellors ready, and assemble the whole thing as shown in the first photo.